The present invention relates to a medical laser apparatus to be used as a light source for a diagnostic/treatment apparatus which treats a focus of a tumor such as a cancer or the like through irradiation of light to the focus. When light having a wavelength coinciding with the absorption wavelength of a photosensitizer which has an affinity to the focus and has been preliminarily accumulated in the focus is irradiated to the focus, the photosensitizer is excited, making it possible to diagnose or treat the focus. The present invention relates alike to a diagnostic/treatment apparatus using the medical laser apparatus.
In accordance with the development of electronic medical-care technology, photodynamic diagnosis (referred to as PDD hereinbelow) and the photodynamic therapy (referred to as PDT hereinafter), each utilizing laser light, have made rapid progress recently. In PDD and PDT, a photosensitizer having affinity to a tumor and capable of a photochemical reaction, e.g., an emission of fluorescence or a cellcidal action is accumulated in a focus of the tumor beforehand, and then light is irradiated to the focus, which induces the excitation of the photosensitizer, to thereby permit diagnosis of the focus by measuring the emitted fluorescence (PDD) or treatment of the focus by the cellcidal action (PDT). It is preferable that the wavelength of the light irradiated to the focus coincides with the absorption wavelength of the photosensitizer in order to efficiently excite the photosensitizer, and therefore a laser light source has been generally employed as a light source of the light irradiating to the focus. In this case, the laser light source is fitted to the absorption wavelength of the photosensitizer being used.
A dye laser which uses hematoporphyrin as a photosensitizer and an excimer laser as a laser light source (referred to as an excimer dye laser hereinbelow) has been often used in the above-described type of diagnostic/treatment apparatus for diagnosing and treating cancers, as is discussed in Japanese Patent Publication Nos. 63-2633 (2633/1988) and 63-9464 (9464/1988). The conventional diagnostic/treatment apparatus using the laser device disclosed in the noted publications will be described with reference to FIG. 4.
FIG. 4 schematically shows the constitution of a cancer diagnostic/treatment apparatus using a conventional laser apparatus. In FIG. 4, A is a focus of a cancer and B indicates the peripheral pair of the focus A where hematoporphyrin has been absorbed as a photosensitizer beforehand. A first pulse source 31 for diagnostic purposes and a second pulse source 32 for treatment purposes are both constituted of an excimer dye laser. An excimer dye laser for exciting the first and second dye lasers 31, 32 repeatedly oscillates with an oscillating wavelength 308 nm and pulse width 30 ns while varying the energy in the range of several mJ–100 mJ. The oscillating wavelength of the first pulse source 31 is 405 nm and that of the second pulse source 32 is 630 nm. The first and second pulse sources 31, 32 are switched by a switching part 33. The other reference numerals represent: 34 a light transmission line; 35 a TV camera; 36 a TV monitor; 37 a half mirror; 38 a spectroscope; 39 a spectrum analyzing part; and 40 a display unit.
The diagnosing/curing apparatus of the above-described constitution operates as follows
When a cancer is to be diagnosed, a laser light of the wavelength 405 nm generated from the first pulse light source 31 is irradiated to the focus A and the peripheral part B through the switching part 33 and the light transmission line 34. A fluorescence image of the wavelength 630 nm, 690 nm excited by the laser light of 405 nm wavelength is photographed by the TV camera 35 and displayed for observation on the screen of the TV monitor 36. At the same time, the fluorescence image is extracted by the half mirror 37 and divided by the spectroscope 38. The spectrum is analyzed in the spectrum analyzing part 39 and the wavelength of the spectrum is displayed by the display unit 40. In order to treat the cancer, then, a laser light of the wavelength 630 nm produced by the second pulse light source 32 is, through the switching part 33 and the light transmission line 34, irradiated to the focus A. The operation mode is subsequently switched to the diagnosing mode again to thereby confirm the result of the treatment. The cancer is diagnosed and treated by repeatedly switching the modes as above.
In addition to the fact that the fluorescence peculiar to hematoporphyrin is efficiently excited by the light of the wavelength 405 nm, adverse influences resulting from scattering light can also be restricted due to the difference of the wavelengths 630 nm and 690 nm of the fluorescence, the first pulse light source 31 for diagnostic purposes thus uses the wavelength 405 nm. Meanwhile, the second pulse light source 32 for treatment purposes is set at the wavelength 630 nm because the laser light of the wavelength 630 nm transmits well through the tissue and is efficiently absorbed in hematoporphyrin.
In addition to the aforementioned example, the photosensitizers in (Table 1) below are proposed for use in PDD and PDT and also the lasers shown in (Table 1) are tried to be used as a laser light source for PDT.
TABLE 1Laser light sourceAbsorption(projection wave-Disadvantages ofPhotosensitizerwavelengthlength [nm])laser devicesHpD630Excimer dye laser*Deterioration ofArgon dye lasersolution of coloring(624 ± 6.5 nm)matter is fast*Bulky and expensiveHpD630Gold Vapor laser*Necessary to warm(627.8 nm)up for 30 mm. ormore*Life of gas andoscillating tube isshort*Bulky and expensivePH-1126650Krypton laser*Life of gas is short(647 nm)*Bulky and expensiveNPe6664Argon dye laser*Deterioration of(667 ± 5 nm)solution of coloringmatter is fast*Bulky and expensive
A drawback of the conventional diagnostic/treatment apparatus of cancers resides in the fact that the wavelength of the projected laser light is difficult to control.
In other words, it is necessary to make the wavelength of the laser light coincident with the absorption band of the photosensitizer so as to efficiently excite the photosensitizer. Generally, it is not possible for the gas laser (Table 1) to meet the absorption band of a plurality of the photosensitizers. Moreover, it is difficult for the gas laser to have a wavelength which coincides with the maximum absorption wavelength of even a single photosensitizer. Although a dye laser as depicted with reference to the above conventional example has been employed to solve the problem, it is necessary to exchange the solution of a coloring matter in order to change the oscillating wavelength of the dye laser. Therefore, a plurality of dye lasers corresponding to a plurality of different kinds of solutions of a coloring matter should be prepared and exchanged for every wavelength if the wavelength of the laser light is required to be changed, for instance, when the photosensitizer being used is changed or when the wavelength of the laser light is changed during treatment relative to that used during diagnoses.
In the case where the dye laser is used, therefore, the diagnostic/treatment apparatus becomes disadvantageously bulky in size to accommodate a plurality of different kinds of coloring matter solutions and a switching of the solutions.
A second disadvantage of the diagnostic/treatment apparatus using the dye laser is that the solution of a coloring matter of the dye laser easily deteriorates, inviting a change of the wavelength of the resultant laser light or a decrease of the output. Since the safety of the laser light is an essential and indispensable condition to ensure the effect of PDD and especially PDT, a substantial problem of the dye laser arises when the solution of the coloring matter should be exchanged or a circulator of the coloring matter should be cleaned frequently. Further, the wavelength of the laser light is undesirably changed or the laser output is decreased during the irradiation if the solution used in the dye laser easily degrades, that is, the irradiating condition of the laser light should be set with such changes in the wavelength or output as above taken into consideration and, the change of the laser light should be arranged to be detected.
Thirdly, when the wavelength is converted by the dye laser, the full width at half maximum (FWHM) of the wavelength of the obtained laser light expands to at least 10 nm or so. If the full width at half maximum is wide, the laser light increasingly shifts from the absorption band of the photosensitizer, thus worsening the exciting efficiency of the photosensitizer. Although it may be arranged to reduce the full width at half maximum of the dye laser by using a band pass filter or a diffraction grating, only the excessive component is cut, but the exciting efficiency is left unimproved.
A fourth drawback is the poor converting efficiency of energy of the dye laser when the wavelength is converted. Therefore, the excimer laser, etc. used as a light source to excite the dye laser is required to generate a high output in order to achieve sufficient energy from the converted laser light. In other words, the conventional medical laser apparatus and the diagnostic/treatment apparatus of cancers using the conventional medical laser apparatus are liable to be bulky and expensive.
A fifth drawback inherent in the prior art resides in the need for two light sources for diagnostic purposes and for treatment purpose as well as the switching mechanism to switch the light sources. The apparatus consequently is bulky and expensive and moreover, it is inconvenient to switch the light sources and erroneous manipulation can occur.